Springest Dev Lunch: MongoDB Introduction

MongoDB
(from “humongous”)

Wouter de Vos – 2011-10-31

What is MongoDB?

• A No-SQL database

• Document oriented

• Open Source

• Written in C++

Document Oriented?

• Documents are stored in collections > db.posts.findOne()
{
_id : ObjectId("4e77bb3b8a3e000000004f7a"),
when : Date("2011-09-19T02:10:11.3Z",
author : "alex",

•
title : "No Free Lunch",
No JOINS: embedded text : "This is the text of the post. It could be very long.",
tags : [ "business", "ramblings" ],
votes : 5,
voters : [ "jane", "joe", "spencer", "phyllis", "li" ],
comments : [

•
{ who : "jane", when : Date("2011-09-19T04:00:10.112Z"),
No JOINS: linked comment : "I agree." },
{ who : "meghan", when : Date("2011-09-20T14:36:06.958Z"),
comment : "You must be joking. etc etc ..." }
]
}

Document Oriented?

• Documents are stored in collections
> db.posts.findOne()

•
{
No JOINS: embedded _id : ObjectId("4e77bb3b8a3e000000004f7a"),
when : Date("2011-09-19T02:10:11.3Z",
author : "alex",
title : "No Free Lunch",
text : "This is the text of the post. It could be very long.",

•
tags : [ "business", "ramblings" ],
No JOINS: linked votes : 5,
voters : [ "jane", "joe", "spencer", "phyllis", "li" ],
comments : [
{ who : "jane", when : Date("2011-09-19T04:00:10.112Z"),
comment : "I agree." },

•
{ who : "meghan", when : Date("2011-09-20T14:36:06.958Z"),
links are references to other documents and ]
comment : "You must be joking. etc etc ..." }

are processed by the client. }

Cool features
> db.invoices.find()
{

• Schemaless
_id : ObjectId("4e77bb3b8a3e000000004f7a"),
client: "Johnson",
hosting: {
per: "month",

•
price: 100,
Atomic operations },
amount: 12,

development: {
per: "hour",

• Map/Reduce
}
price: 120,
amount: 80

},

•
{
Fast, in-place updates _id : ObjectId("4e77bb3b8a3e000000005f7a"),
client: "Black",
development: {
per: "hour",

• GridFS
}
price: 120,
amount: 30

},

Cool features
• Schemaless atomically {
if( doc.credits > 5 ) {
doc.credits -= 5;
• Atomic operations doc.debits += 5;
}
}
• Map/Reduce

• Fast, in-place updates

• GridFS

Cool features
// Document example
{ username: "jones",
likes: 20,
text: "Hello world!"

• Schemaless }

// Map
function() {

• Atomic operations }
emit( this.username, {count: 1, likes: this.likes} );

// Reduce

•
function(key, values) {
Map/Reduce var result = {count: 0, likes: 0};

values.forEach(function(value) {
result.count += value.count;

• Fast, in-place updates result.likes += value.likes;
});

return result;

•
}
GridFS
// Result
{ count: 10, likes: 247 }

Cool features
• Schemaless

• Atomic operations
// In place update
db.recipes.update(

• Map/Reduce
)
{'_id': recipe_id, 'voters': {'$ne': user_id}},
{'$inc': {'votes': 1}, '$push': {'voters': user_id}}

• Fast, in-place updates

• GridFS

Cool features
• Schemaless

• Atomic operations The GridFS spec provides a mechanism for
transparently dividing a large file among multiple

• Map/Reduce
documents. This allows us to efficiently store large
objects, and in the case of especially large files,
such as videos, permits range operations (e.g.,
• Fast, in-place updates fetching only the first N bytes of a file).

• GridFS

Querying
• // A post with title “Mongo”
db.posts.find({'title': 'Mongo'})

• // All posts about tennis, but without comments
db.posts.find( { tags : 'tennis' }, { comments : 0 } );

• // last 5 comments
db.posts.find({}, {comments:{'$slice': -5}})

• // just the likes of the comments
db.posts.find({}, {'comments.$.likes': 1}

Use it for

• It’s schemaless features (e.g. for prototyping)

• It’s horizontal scalability (with auto-sharding)

• To store and stream large ﬁles (with gridfs)

• To make ultra-fast, single query updates

Scenarios for browser testing
Feature: User Registration and Logging in
A User should be able to create an account.
A User should be able to log in with a new account.
A User should be able to create a profile after logging in for the first time.

Scenario: Registration with a normal account.
Given I sign up as a new user with email@example.com/secret
Then I should be signed in
And I sign out

Scenario: Log in with a new account
Given I sign up as a new user with email@example.com/secret
Then I sign out
And I sign in with email@example.com/secret
And I sign out

Scenario: Create a profile with a new account
Given I sign in as a new user
Then I should see "create your profile"
And I fill in "profile_name" with "My Name"
And I fill in "profile_about" with "I am a long green vegetable that goes well with salads."
And I select an avatar file
And I press "Save"
Then I should see "Profile was successfully updated."
And I sign out

Mechanize, Selenium / Webkit

• Mechanize: fast, but no javascript support

• Selenium, javascript support, but sloooow

• Webkit, javascript support, less slooow

Springest Dev Lunch: MongoDB Introduction

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Editor's Notes